[rescue] Re: [SunHELP] Help with RAID

[Phil Stracchino]

On Thu, Jun 05, 2003 at 12:18:07AM -0400, Curtis H. Wilbar Jr. wrote:
> Ummm... everywhere I've ever done this, you create either two stripes
> which you then mirror, or two concats and then mirror.... I've never
> heard of someone concatenating a bunch of little mirrors...

Concating mirrors obviously makes no sense.  Striping mirrors does.
Think about it.


> >Here's an example of the metainit commands to do it:
> >
> >metainit d11 1 10 c1t{0,1,2,3,4,5,6,7,8,9}d0s0 -i 128k
> >metainit d12 1 10 c2t{0,1,2,3,4,5,6,7,8,9}d0s0 -i 128k
> >metainit d10 -m d11
> >metattach d10 d12
> 
> This is creating a mirror of two stripes !

That's what the commands do, yes.  I am advised that Disksuite
recognizes at this point what you're trying to do, and juggles things
internally to end up with striped mirrors instead of mirrored stripes.

The guy who told me this wrote ORA's System Performance Tuning, Second
Edition, and I have pretty good confidence that he knows what he's
talking about.

> Are you sure about this ?  I'd like to know more about it and the source,
> becasue I worked for Sun, have friends that work for Sun, have used Disk Suite
> since the SunOS 4.X days and I have never heard of this.

See above.  :)

(He's no longer at Sun, but writes a regular performance-tuning column
for ORA now and can probably be contacted there.)


> If you have the CPU... you'll get more space by going with RAID 5,
> but your I/O throughput will go down.  Another instance of space vs speed.
> 
> -- Curt

Indeed.  Everything's a trade-off.


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